The invention relates to metering devices, and particularly to metering devices measuring the flow of material in a pipe. Specifically, the invention relates to a method and apparatus for determining and indicating the data that is related to the quantity of solids conveyed in a solid-liquid slurry that is flowing in a pipe.
The invention has application in numerous fields where solids are moved or transported in a slurry in a pipe system, such as, but not limited to, the coal industry, dredging operations, mining and quarrying, and other similar or comparable material handling situations. For illustrative purposes, several comments are directed toward uses in the dredging industry as this is one of the primary fields of application. The illustrations may have similar or comparable application to the other industries.
Present practice for dredge production instrumentation is to use a nuclear density gauge to measure slurry specific gravity and either an elbow meter, or a magnetic flowmeter to measure velocity. U.S. Pat. No. 3,926,050 describes such a method and apparatus.
One major disadvantage of the aforementioned systems has been the license requirement and legal restriction associated with the transportation and use of nuclear equipment and materials. The primary objective of this invention is to provide an alternative system which replaces the nuclear gauge with a combination of two commerically available sensors, a differential pressure transmitter and an ultrasonic doppler flowmeter, hereinafter referred to as a sonic flowmeter.
The invention provides a means for measuring the weight or quantity of particles moving over a period of time. It can also measure the velocity of the slurry as a separate readout.
While the flowmeter described is of the ultrasonic doppler type, favored because of its cost advantage, this is not intended to exclude other types of flowmeters that are not significantly affected by slurry specific gravity, such as the magnetic flowmeter, which is used at present, and other types of sonic flowmeters.
This invention includes the equipment necessary to combine the output signals from the differential pressure transmitter and the sonic flowmeter, perform the mathematical calculations, and display the data related to the quantity of solids conveyed.
Sonic flowmeters particularly, and to a lesser extent the other types of flowmeters not affected by slurry specific gravity, are very sensitive to local variations of velocity within a pipe. For coarse sand and gravel moving at relatively low velocities in a horizontal pipe, the sand and gravel moves slowly along the bottom of the pipe while nearly clear water flows at a higher velocity above the solids. The doppler ultrasonic flowmeter works by bouncing sound waves off of the solid particles and measuring particle velocity. Erratic results are obtained if the sonic flowmeter's sensor is located near the bottom of the pipe due to low velocity of the solids and also due to the high concentration of solids there. When the sensor is located near the top of the pipe, the flowmeter indicates a velocity much higher than the desired average velocity of slurry within the pipe. Thus, under the conditions described, sonic flowmeter indication is unsatisfactory for most applications.
Only at several specific locations or by using several special devices, all of which are included in this invention, does the sonic flowmeter give an accurate indication of average slurry velocity, at least under the conditions described. Results are satisfactory for most solids in a vertical pipe that is well removed from any elbows or fittings, rarely available in dredging systems, or for fine sand at high velocity.
Exceptional accuracy is required of both the density-sensitive flowmeter (elbow meter) and density-insensitive flowmeter (sonic) when the signals are combined to determine the slurry's specific gravity. The reason for this is apparent from a consideration of a slurry having 1.111 specific gravity. Only ten percent of the elbow meter's differential pressure is due to the presence of solids in the slurry. Since, as shown hereinafter, the sonic flowmeter's signal is squared, just a five percent error in this signal could cause an indication of 1.00 specific gravity, indicating falsely that no solids were being pumped or moved in the pipe.
It is, therefore, an object of the invention to provide a method and apparatus for determining solids being conveyed in a slurry that is moving in a pipe.
It is another object of the invention to provide a method and apparatus for determining solids being conveyed in a slurry that is moving in a pipe that does not use nuclear gauging equipment.
It is also an object of the invention to provide a method and apparatus for determining solids being conveyed in a slurry that is moving in a pipe that uses a combination of two commercially available sensors.
It is still another object of the invention to provide a method and apparatus for determining solids being conveyed in a slurry that is moving in a pipe by using a differential pressure transmitter and an ultrasonic doppler flowmeter.
It is yet another object of the invention to provide a method and apparatus for determining solids being conveyed in a slurry that is moving in a pipe by providing the optimum locations and positions for both the elbow meter and the sonic flowmeter sensors, including a special calibration procedure.
It is also another object of the invention to provide a method and apparatus for determining solids being conveyed in a slurry that is moving in a pipe by automatically performing the mathematical calculations and displaying the data.
Further objects and advantages of the invention will become more apparent in the light of the following description of the preferred embodiments.